Pension Plan and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pension Plan
Pension Plan and Other Postretirement Benefits
Employer cash contributions			$ 2,900	$ 8,800
Estimated cash contributions in the current fiscal year	$ 2,900		2,900
Components of the pension plans and other postretirement benefits
Service cost	6,046	$ 9,235	12,092	18,470
Interest cost	8,746	6,329	17,492	12,658
Expected return on plan assets	(13,421)	(11,307)	(26,842)	(22,614)
Amortization of prior service cost	131	242	262	484
Recognized net actuarial (gain) loss	(637)	999	(1,274)	1,998
Net periodic benefit cost (benefit)	865	5,498	1,730	10,996
Other Benefits
Pension Plan and Other Postretirement Benefits
Employer cash contributions			200	300
Estimated cash contributions in the current fiscal year	200		200
Components of the pension plans and other postretirement benefits
Service cost	1,126	1,683	2,252	3,366
Interest cost	1,297	1,008	2,595	2,016
Expected return on plan assets	(2,636)	(2,482)	(5,271)	(4,964)
Amortization of prior service cost	39	39	77	78
Recognized net actuarial (gain) loss	(581)	(228)	(1,163)	(456)
Net periodic benefit cost (benefit)	$ (755)	$ 20	$ (1,510)	$ 40